| Abstract
| - We present new results for the water dimer equilibrium constant Kp(T) in the range 190−390 K, using aflexible potential energy surface fitted to spectroscopical data. The increased numerical complexity due toexplicit consideration of the monomer vibrations is handled via an adiabatic (6 + 6)d decoupling betweenintra- and intermolecular modes. The convergence of the canonical partition function of the dimer is ensuredby computing all energy levels up to dissociation for total angular momentum values J = 0−5 and using anextrapolation scheme to higher values. The newly calculated values for Kp(T) are in very good agreementwith available experimental data at room temperature. At higher temperatures, an analysis of the convergenceof the partition function reveals that quasi-bound states are likely to contribute to the equilibrium constant.Additional thermodynamical quantities (ΔG, ΔH, ΔS, and Cp) have also been determined and fit to quadraticexpressions a + bT + cT2.
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